Step-up converters are used in particular in photovoltaic installations for adapting the DC voltage of individual strings to the DC voltage of a common intermediate circuit. In this case, operation of the step-up converter with the best possible efficiency is desirable to avoid energy losses and to reduce the outlay for cooling the components of the step-up converter, in particular a semiconductor switch of the step-up converter. It is known from resonance converters, for example, that low-loss switching of the semiconductor switch can be achieved by the switch being switched at points in time at which the switch is free of current or free of voltage. This is referred to as soft switching.
The document DE2639589A1 discloses a step-up converter with an arrangement of an inductance, a step-up converter switch and a step-up converter diode between DC voltage inputs and DC voltage outputs as it is conventional for step-up converters. The step-up converter comprises a snubber circuit having a charging path and a discharging path, wherein the discharging path runs as a series connection of a capacitor and a diode in parallel with the step-up converter diode. Via the charging path, which comprises a series connection of a further diode and a further inductance and one end of which is connected to a junction point between the capacitor and the diode, the capacitor is charged when the step-up converter switch is switched on, for which purpose a voltage at an amount of half the output voltage of the step-up converter is applied to the other end of the charging path. Concerning this, the document DE2639589A1 discloses that the charging path can be connected to the center point of a divided output capacitance between the DC voltage outputs, and for this furthermore it discloses a compensation circuit that can be used to compensate for an unequal discharge of the two capacitances of the divided output capacitance that is caused by the charging circuit.
The document U.S. Pat. No. 7,385,833B2 likewise discloses a step-up converter with the arrangement of an inductance, a step-up converter switch and a step-up converter diode between DC voltage inputs and DC voltage outputs as it is conventional for step-up converters. The step-up converter comprises a snubber circuit having a charging path and a discharging path, wherein the discharging path runs as a series connection of a capacitor and a diode in parallel with the step-up converter diode, and wherein the charging path, one end of which is connected to a junction point between the capacitor and the diode, comprises a series connection of a further diode and a further inductance. The other end of the charging path is connected to a line of the step-up converter that connects one of the DC voltage inputs to one of the DC voltage outputs. In order to charge the capacitor when the step-up converter switch is switched on, the further inductance in the charging path is magnetically coupled to the inductance of the step-up converter. The energy for charging the capacitor is thus drawn from an energy source connected to the DC voltage inputs.
The document US20080094866A1 discloses using a step-up converter with the arrangement of an inductance, a step-up converter switch and a step-up converter diode between DC voltage inputs and DC voltage outputs as it is conventional for step-up converters. The step-up converter comprises an actively switched snubber circuit, in conjunction with a photovoltaic generator.